A number of medical conditions such as compression of spinal cord nerve roots, degenerative disc disease, tumor, and trauma can cause severe back pain. Intervertebral fusion is one surgical method of alleviating back pain. In intervertebral fusion, two adjacent vertebral bodies are fused together by removing the affected intervertebral disc and inserting an implant that would allow for bone to grow between the two vertebral bodies to bridge the gap left by the disc removal. Another surgical method of relieving back pain is by corpectomy. In corpectomy, a diseased or damaged vertebral body along with the adjoining intervertebral discs are removed and replaced by a spinal implant that would allow for bone to grow between the closest two vertebral bodies to bridge the gap left by the spinal tissue removal.
A number of different implant materials and implant designs have been used for interbody fusion and for vertebral body replacement with varying success. Current implant materials used include metals, radiolucent materials including plastics, elastic and polymeric materials, ceramic, and allografts. Current implant designs vary from threaded cylindrical implants to rectangular cages with teeth-like protrusions.
For example, U.S. Pat. No. 5,782,919 to Zdeblick et. al. discloses an interbody fusion device which has a tapered body defining a hollow interior for receiving a bone graft or bone substitute material. Furthermore, the body of the device defines exterior threads for gripping the adjacent vertebrae and has a series of vascularization openings for promoting bony ingrowth. A variant on this design is shown in U.S. Pat. No. 4,961,740 to Ray et, al. The Ray patent illustrates a hollow, cylindrical fusion cage having a helical thread disposed on the outer surface of the cage with a plurality of holes leading to the hollow center between the threads.
U.S. Pat. No. 5,766,252 to Henry et. al. discusses a rectangular interbody spinal spacer that has vertically opposite upper and lower load bearing surfaces spaced apart a distance corresponding to the desired spacing. The rigid member has a wedge-shaped configuration with an ogival tip at the front end of the member.
While each of the foregoing prosthesis, address some problems relating to intervertebral disc replacements or vertebral body and intervertebral disc replacements, they present others. Thus, there is a need for an intervertebral implant whose design takes into consideration the anatomy and geometry of the intervertebral space sought to be filled by the intervertebral prosthesis as well as the anatomy and geometry of the end plates of the adjacent vertebral bodies. There is also a need for a spinal disc implant which integrates well with the vertebral bone tissue of the adjacent vertebral bodies between which the implant is to be inserted.